1. Field of the Invention
Embodiments of the present invention generally relate to methods for forming device structures for thin film transistor applications. More particularly, this invention relates to methods and sequences for forming device structures for thin film transistor applications.
2. Description of the Related Art
Plasma display panels, active matrix liquid crystal displays (AMLCD) or active matrix organic light emitting diodes (AMOLED) and liquid crystal displays are frequently used for flat panel displays. Liquid crystal displays (LCD) generally contain two transparent substrates joined together with a layer of a liquid crystal material sandwiched therebetween. The transparent substrate may be a semiconductor substrate, glass, quartz, sapphire, flexible or a clear plastic film. The LCD may also contain light emitting diodes for back lighting.
As the resolution requirements for liquid crystal displays increase, it has become desirable to control a large number of separate areas of the liquid crystal cell, called pixels. In a modern display panel, more than 1,000,000 pixels may be present. At least the same number of transistors is formed on the glass substrate so that each pixel can be switched between an energized and de-energized state relative to the other pixels disposed on the substrate.
FIG. 1 depicts a sequence of manufacturing a conventional thin film transistor device. FIGS. 2A-2D depicts the conventional thin film transistor device at different manufacture stages manufactured by the sequence depicted in FIG. 1. Generally, the thin film transistor device 200 is disposed on a substrate 202, as depicted in FIG. 2A. A gate electrode 204 is formed and patterned on the substrate 202 followed by a gate insulator layer 206. An active layer 208 is formed on the gate insulator layer 206. The active layer 208 is often selected from a transparent metallic oxide material that has high electron mobility as well as low temperature manufacture process requirements to allow the use of flexible substrate materials, such as plastic materials, to be processed at low temperatures to avoid substrate damage. After formation of the active layer 208, an etching stop layer 210 is formed on the active layer 208. Subsequently, a source-drain metal electrode layer 214 is then disposed thereon to form the thin film transistor device 200 having a region 218 exposed through a patterned photoresist layer 216 to form a channel therein during the subsequent etching and patterning processes.
Referring back to FIG. 1, after the device structure 200 is formed on the substrate 202, at step 102, the substrate 202 is then transferred to a metal active layer patterning tool to perform a metal active layer patterning process to remove unprotected regions 230 of the active layer 208 from the device structure 200 to expose exposing regions 226 of the underlying gate insulator layer 206, as shown in FIG. 2B. It is noted that the unprotected regions 230 of the active layer 208 may or may not be damaged by the previous process, as shown as an uneven surface in FIG. 2A. After the metal active layer patterning process, at step 104, a back-channel-etching (BCE) process is performed to etch the source-drain metal electrode layer 214 to form a channel 228 in the thin film transistor device 200 until an upper surface 220 of the underlying etch stop layer 210 is exposed, as shown in FIG. 2C. During the back-channel-etching (BCE) process, the aggressive etchants utilized during the etching process may adversely etch and attack the underlying active layer 208 of the device 200, resulting in damage and undesired edge profile 222 in the active layer 208, thereby deteriorating film quality and electric performance of the thin film transistor device 200. At step 106, the substrate 202 is then transferred to a photoresist layer removal processing tool to remove the photoresist layer 216, as shown in FIG. 2D. During the photoresist layer removal process, the edge 222 of the active layer 208 may be further damaged or attacked during the subsequent process along with other passivation and patterning process performed at step 108 to complete the device manufacture process, thereby adversely deteriorating film quality of the active layer 208 and leading to device failure.
Therefore, there is a need for a method for manufacturing the thin film transistor devices having improved electrical performance and stability.